sched/numa: Be more careful about joining numa groups

Due to the way the pid is truncated, and tasks are moved between
CPUs by the scheduler, it is possible for the current task_numa_fault
to group together tasks that do not actually share memory together.

This patch adds a few easy sanity checks to task_numa_fault, joining
tasks together if they share the same tsk->mm, or if the fault was on
a page with an elevated mapcount, in a shared VMA.

Signed-off-by: Rik van Riel <riel@redhat.com>
Signed-off-by: Mel Gorman <mgorman@suse.de>
Cc: Andrea Arcangeli <aarcange@redhat.com>
Cc: Johannes Weiner <hannes@cmpxchg.org>
Cc: Srikar Dronamraju <srikar@linux.vnet.ibm.com>
Signed-off-by: Peter Zijlstra <peterz@infradead.org>
Link: http://lkml.kernel.org/r/1381141781-10992-57-git-send-email-mgorman@suse.de
Signed-off-by: Ingo Molnar <mingo@kernel.org>

1 files changed, 7 insertions, 0 deletions

diff --git a/mm/memory.c b/mm/memory.c
index 9898eeb9a21c..823720c43ea9 100644
--- a/mm/memory.c
+++ b/mm/memory.c
@@ -3584,6 +3584,13 @@ int do_numa_page(struct mm_struct *mm, struct vm_area_struct *vma,
         if (!pte_write(pte))
                 flags |= TNF_NO_GROUP;
 
+        /*
+         * Flag if the page is shared between multiple address spaces. This
+         * is later used when determining whether to group tasks together
+         */
+        if (page_mapcount(page) > 1 && (vma->vm_flags & VM_SHARED))
+                flags |= TNF_SHARED;
+
         last_cpupid = page_cpupid_last(page);
         page_nid = page_to_nid(page);
         target_nid = numa_migrate_prep(page, vma, addr, page_nid);